Algae

Kingdom Protista — Overview

  • Domain: Eukarya.

  • Includes very diverse organisms:

    • Unicellular → multicellular.

    • Microscopic → giant kelp.

  • First eukaryotes (~1.5 billion years ago).

  • Live in moist environments.

  • Can be free-living or symbiotic.

Three Types of Protists

  1. Animal-like protists (protozoa) — ingest food.

  2. Plantlike protists (algae) — photosynthetic.

  3. Funguslike protists — decomposers.

Modern Classification Issue

  • Protista = paraphyletic group (not all descendants included).

  • Some protists more related to plants, animals, fungi than each other.

Plantlike Protists (Algae) — Key Characteristics

  • Contain chlorophyll → photosynthesis.

  • Autotrophic (make own food).

  • Can be:

    • Unicellular

    • Multicellular

    • Colonial

  • Mostly aquatic (freshwater or marine).

  • Base of aquatic food chains.

  • Produce large amounts of Earth’s oxygen.

  • Some macroscopic (seaweed, kelp).

Photosynthetic Pigments

Chlorophyll

  • Captures light energy.

  • Types: chlorophyll a, b, c.

Accessory Pigments

  • Absorb additional wavelengths.

  • Give algae different colors:

    • Red

    • Brown

    • Gold

  • Adaptation for low-light underwater environments.

Major Algae Groups

Unicellular Algae

1. Euglenophytes

  • Freshwater.

  • Flexible cell covering (pellicle).

  • Eyespot detects light.

  • Flagella → movement.

  • Can be:

    • Autotrophic (photosynthesis).

    • Heterotrophic (absorb nutrients if no sunlight).

  • Reproduce by binary fission.

  • Contractile vacuole removes excess water.

2. Chrysophytes (Golden Algae + Diatoms)

  • Yellow-green or golden-brown.

  • Pigment: fucoxanthin.

  • Cell walls: cellulose + pectin.

  • Can be autotrophic or heterotrophic.

  • Store food as oil.

  • Diatoms:

    • Silica cell walls.

    • Form diatomaceous earth → filters, abrasives.

3. Dinoflagellates

  • Part of plankton.

  • Two flagella.

  • Cellulose plates.

  • Some glow (bioluminescence).

  • Can be:

    • Autotrophs

    • Heterotrophs

    • Parasites

    • Endosymbionts

  • Cause ocean phosphorescence.

Multicellular Algae

Why Multicellularity Evolved

  • Stay near shore for nutrients.

  • Developed:

    • Holdfasts → anchor.

    • Air bladders → float.

4. Red Algae (Rhodophytes)

  • Mostly marine.

  • Pigment: phycobilins (red).

  • Can live in deep water.

  • Cell walls contain agar and carrageenan.

  • Store food as Floridean starch.

  • Used for:

    • Food (nori).

    • Culture media.

    • Stabilizers.

  • Important for coral ecosystems.

5. Brown Algae (Phaeophytes)

  • Marine, cool waters.

  • Pigment: fucoxanthin.

  • Includes giant kelp (up to 30 m).

  • Structures:

    • Blades (leaflike).

    • Holdfasts.

    • Air bladders.

  • Store laminarin.

  • Produce alginates → thickening agents.

  • Form productive kelp forests.

6. Green Algae (Chlorophytes)

  • Mostly freshwater.

  • Chlorophyll a + b.

  • Store starch.

  • Cell walls of cellulose.

  • Forms:

    • Unicellular

    • Colonial

    • Multicellular

  • Examples: Spirogyra, Volvox, Ulva.

  • Likely ancestors of land plants.

Green Algae Reproduction

Alternation of Generations

  • Haploid gametophyte (n) → produces gametes.

  • Fertilization → diploid sporophyte (2n).

  • Sporophyte produces spores by meiosis.

  • Cycle repeats.

Important evolutionary link to land plants.

Ecological Importance of Algae

  • Primary producers in aquatic ecosystems.

  • Produce major portion of Earth’s oxygen.

  • Provide habitat for marine organisms.

  • Form productive ecosystems (kelp forests).

  • Base of aquatic food chains.

Harmful Effects

  • Algal blooms / red tides:

    • Release toxins.

    • Kill marine life.

    • Harm food supply.

Human Uses of Algae

  • Food (seaweed).

  • Agar → lab cultures.

  • Carrageenan → food stabilizer.

  • Alginates → cosmetics, medicine, textiles.

  • Filters and abrasives (diatomaceous earth).

Algae and Climate Research

  • Remove CO₂ through photosynthesis.

  • Biological pump:

    • Carbon moves to deep ocean.

  • Studied for climate regulation.

AP Biology Big Ideas

  • Evolution of eukaryotes.

  • Endosymbiosis and diversity.

  • Adaptations to environment.

  • Photosynthesis and energy capture.

  • Ecosystem energy flow.

  • Alternation of generations.

  • Link between algae and land plants.